1. Field
The present disclosure relates to an oxynitride phosphor, methods of preparing the oxynitride phosphor, and white light emitting devices including the oxynitride phosphor, and more particularly, to an oxynitride phosphor having excellent color rendering properties and color reproduction properties.
2. Description of the Related Art
An optical illumination system may include a fluorescent lamp or an incandescent lamp. Fluorescent lamps, however, cause environmental problems due to mercury (Hg) included therein. Also, such optical illumination systems have very short lifetimes and low efficiency and thus are unsuitable for energy saving applications. Therefore, much research is being performed to develop a white light emitting device having high efficiency.
Improved white light emitting devices may produce white light using the three following methods. Red, green, and blue phosphors may be excited using an ultra violet (“UV”) light emitting diode (“LED”) light source to produce white light, red and green phosphors may be excited using a blue LED light source to produce white light, or a yellow phosphor may be excited using a blue LED light source to produce white light.
However, a method of producing white light by exciting a single white phosphor using a UV LED light source has not yet been developed. In this method, color rendering properties may be improved by avoiding a situation wherein light with a wavelength around 480 nanometers (nm) is not provided, compared to a general method in which a blue LED and a yellow phosphor or a blue LED and a green phosphor are used. In addition, undesirable reabsorption, which may occur when using two or three phosphors, may be avoided. Even if the single white phosphor is used together with another phosphor, excellent color rendering properties may be obtained by virtue of a large half width value, compared to an embodiment wherein a white phosphor is not used.
Nitride phosphor preparation methods known hitherto require process conditions of high temperature and high nitrogen gas pressure (more than 0.1 megapascals, MPa). Thus, a special apparatus designed to withstand high temperature and high pressure is desirable. Moreover, unstable materials are used as starting materials, and thus, the stringency of conditions recommended to handle the starting materials increases.